Neutrally Buoyant Sensor Node Shear Wave Noise Reduction
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Solution Overview
Problem
Particle motion sensors in marine seismic surveys face significant noise and interference from shear forces and cable dynamics, which diminish the accuracy of particle velocity readings due to the similar magnitudes of shear waves and acoustic waves passing through the water column.
Innovation Solution
An autonomous, neutrally buoyant spherical sensor node is designed to float above the seafloor, minimizing shear wave noise contamination by using a tether that prevents the transfer of shear forces and maintaining the sensor's center of gravity at its geometric center, allowing it to measure seismic pressure waves and water-borne particle velocity in three dimensions with reduced noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If particle motion sensors are deployed on the seafloor or attached to cables, then they can detect seismic waves, but they experience significant noise and interference from shear forces and cable dynamics
Solution Approach 1:
The patent introduces water as an intermediary medium between the sensor and the seafloor. The sensor is suspended in water by a tether, allowing it to detect acoustic waves through the water column while the tether acts as a mechanical filter that blocks shear forces from the seafloor from reaching the sensor. This intermediary approach enables the sensor to measure particle velocity in the water column without direct contact with shear-wave-generating surfaces.
Solution Approach 2:
The patent replaces traditional mechanical seafloor-mounted sensors with a buoyant sensor system that uses acoustic wave propagation through water instead of direct mechanical contact with the seafloor. By substituting the mechanical coupling mechanism (direct seafloor contact) with an acoustic field-based approach, the system can detect seismic waves while immune to shear force contamination.
2Stability of the object's composition
If the sensor is attached to a tether to maintain position, then it can remain stationary, but shear forces still propagate through the tether to the sensor
Solution Approach 1:
The tether serves as a selective intermediary that transmits only vertical acoustic forces from the water column to the sensor while blocking horizontal shear forces from the seafloor. The tether's mechanical properties and its suspension configuration create a force transmission path that is sensitive to acoustic pressure waves but insensitive to shear wave vibrations, effectively filtering out harmful shear force transmission.
3Object-affected harmful factors
If the sensor floats above the seafloor to avoid shear forces, then noise is reduced, but the sensor must be attached to an anchor which still transmits shear forces
Solution Approach 1:
The tether acts as a mechanical filter that differentiates between vertical acoustic forces and horizontal shear forces. By suspending the sensor from the tether rather than anchoring it directly to the seafloor, the system allows the sensor to float above the seafloor and experience reduced shear wave noise while the tether selectively transmits only the vertical acoustic component needed for particle velocity measurement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The neutrally buoyant sensor node significantly reduces shear wave noise, enhancing the accuracy of particle velocity measurements by isolating the sensor from seabed forces and allowing for more precise geophysical data acquisition in marine seismic surveys.
Implementation Method 1
An autonomous, neutrally buoyant spherical sensor node is designed to float above the seafloor
Implementation Method 2
measuring seismic pressure waves and water-borne particle velocity in three dimensions
Data Source
AI summary
An autonomous sensor node for undersea seismic surveying is formed as a sphere with density similar to sea water in order to minimize effects of noise. The node is capable of measuring both seismic pressure waves and water-borne particle velocity in three dimensions. The node floats above the seafloor to greatly decrease the impact of shear wave noise contamination generated by seabed waves. The node is attached to an anchor resting on the seabed by a tether. The tether is configured to prevent transfer of any tensile forces caused by shear waves in the seabed stratum from the anchor to the node. The tether may have a varying density along its length to entirely attenuate any force transfer from the seafloor.